The adaptive modulation scheme is good-known as a method for keeping high-speed communication while maintaining communication quality. The adaptive modulation scheme selects an optimum modulation scheme depending on condition of a transmission path. Patent Document 1 describes the technology in which adaptive modulation is conducted by determining line condition using a CNR (Carrier to Noise Ratio, i.e. carrier-wave power to signal power ratio) in a wireless transmission device using the adaptive modulation scheme. Patent Document 1 discloses a communication device which uses the CNR as communication quality information and selects a modulation scheme by comparing the CNR with a determination threshold value.
Patent Document 1 discloses a communication device which estimates speed of change of propagation path condition based on a fading pitch (occurrence cycle of fading) and selects an estimation method of communication quality depending on the result thereof.
The communication device described in Patent Document 1 improves transmission efficiency by selecting a modulation scheme based on communication quality estimated by the selected method.